Single crystal growth method

ABSTRACT

In the present invention a signal is caused to fall on the molten liquid surface of single crystal raw material which was put into a crucible, the position of the molten liquid surface is measured by detecting the reflected signal coming from the molten liquid surface and the crucible is lifted according to the discrepancy to the set value.

FIELD OF THE INVENTION

The present invention relates to an improvement on a procedure forgrowing a single crystal in accordance with the Czochralski method(hereafter abbreviated as the CZ method).

PRIOR ART

As a process for manufacturing such crystals as silicon single crystals,a method known as the CZ method for growing single crystal is generallybeing used. In this method, the crystalline raw material that has beenplaced into the crucible is melted and, following contact of the seedcrystal with the molten liquid, while the seed crystal and the cruciblerotate in opposite direction to each other, resulting the seed crystalgrowing.

In an existing similar single crystal growth method, when the crystal ispulled up, the molten liquid level decreases and the surface of themelt, i.e. the condition of the single crystal growth surface, isaltered thus after a while the single crystal comes to a point where itcannot be pulled up. Additionally, when the molten liquid level shifts,the quantity of oxygen dissolved from the molten liquid also changes,thus the axial oxygen concentration of the single crystal obtained isaltered as well. Recently, an IG (Intrinsic Gettering) process whichmakes use of the oxygen precipitates has come into effect requiring astrict control over the oxygen concentration.

In dealing with this problem, the prior art carried out control of themolten liquid level using only a rate controller. The present processattempts to maintain the position of the molten liquid level incountering the crystal pulling up speed by fixing the lifting of thecrucible at a constant speed such that volume of the displaced liquidportion is properly offset.

But in the prior art when drawing up single crystals using an automaticdiameter controller, in the initial stages, during what is-known as"shoulder forming" before the body section of the crystal becomes fixedin diameter, the ratio of the rate controller is too small and theuniformity of the liquid level cannot be maintained. Thus, as a result,the precise liquid level corresponding to the constant section of thecrystal could not be established. Furthermore, the thermal deformationthat occurs at the single crystal pulling temperature in addition tochange in the interior volume of the crucible both produced variation ofthe melt level. Consequently, through just the use of the aforementionedrate controller, precise control of the melt level was not possible inthis prior method. Additionally, the oxygen concentration of the singlecrystal depends on both the temperature of the melt surface and thecooling rate of the crystal. Control of both, the amount of flow of theargon gas covering the liquid surface and the quantity of silicideevaporation were essential as was the precise control of the melt levelposition during the entire pulling period, from beginning to end.

However, in the CZ method, during the "seed" process in which the seedcrystal is dipped into the melt and tapered upon pull up, if thetemperature of the melt following melting of the raw material is evenslightly off, dislocation-free crystal pulling is not possible. As aresult, in this CZ method, after perfectly melting the raw material andovershooting 1500° C., it was essential to calm down the melt andstabilize the molten liquid convection inside the crucible.Additionally, it was essential that the oxygen concentration be fixed ata constant level at the melt surface in the initial pull up stage.However, the interior of the heat furnace is kept at an extremely hightemperature and a thermometer cannot be set up, thus, in the prior art,detection of the melt temperature depends on the operator's perception.In actuality, the dipping and tapering draw up of the seed crystal wascarried out using this detection method. But in the aforementionedprocess in which detection depends on the operator's perception, it isvery difficult to measure precisely the temperature of the liquid. Aswell, an enormous amount of time is taken leading up to theaforementioned "seed" process, in addition to the fact that automationof the process is very difficult once the oxygen concentration of theinitial stage is fixed at a constant value.

On the other hand, a method for indirectly estimating the molten liquidtemperature by measuring the temperature of the carbon heater through aclear window, built into the outer container of the heat furnace, isalso being used (First Publication Laid open number 63-107888). However,time is required for the liquid temperature to reach the temperature ofthe heater (i.e. due to the existence of time lags). In this process,the liquid temperature is actually controlled in accordance with theprofile of the fixed time and temperature: establishing a fixedtemperature was difficult. Moreover, a separate method exists in which asingle spectormeter is used to directly measure the melt temperaturethrough the clear window that was built into the container surface ofthe heat furnace. However, in this method, fluctuations in thetemperature of the molten liquid at the time of melting producesclouding of the window due to the gas of the raw material gas from themelt surface. Thus the power of the spectrometer was susceptible tofluctuations and the method was liable to frequent error.

Additionally, there exists a PID control method for controlling thefixed temperature of the melt (proportional, integral, derivativecontrol). In this PID control, the detection temperature, which is basedon a appropriately established parameter, gives feedback to theelectrical power of the heater. The parameter can then be adjustedfurther using the control result of the previous parameter. But when thecondition of the PID control in the initial stage was unstable a numberof disadvantages resulted: precise control was not possible and a greatamount of time was needed to reach the optimum parameter. In addition,the time-fixed temperature was greatly separated from the temperature ofthe melt and the process became susceptible to overshooting.

In the manufacturing of single crystals in the prior art, among thevarious conditions for operating the draw up furnace, such things as thespeed of pull up (in particular the growing speed of the crystal) andthe heater temperature were automatically recorded on paper, but theother conditions were checked by the eye of the operator using standardset points.

But among the silicon single crystals manufactured in the mannerdescribed above, the solidification of the crystal produces manydrawbacks such as point defects, or inconsistencies in the oxygen andcarbon concentrations. It is known that these inconsistencies are theprimary causes of fluctuations in the conditions at the time of pull up.However, the allowable sphere of these inconsistencies is not somethingthat can be decided as a rule. This is because depending on theconditions under which the semiconductor is manufactured, the singlecrystal used will undergo many different heat histories, up until theend of the process, the oxygen precipitates fall within the limits ofthe field. The conditions come to demand the maintenance of the waferstrength, each kind manufactured for the customer is different as theconditions demand; and until the end of the process the precipitation ofthe oxygen has to be in an appropriate range, the strength of the waverhas to be maintained and the necessary conditions varying with each kindof product for the customer are directed.

The radial distribution of the oxygen density becomes a problem, theoxygen precipitation depending on the density difference between theinner and surrounding part becomes nonuniform, a decline in the yield ofthe semiconductor chips and a warpage thereof occurs, production andtransport equipment for semiconductors cannot be operated and it becomesobvious that a continued production becomes impossible.

Furthermore, when specific IC semiconductors are produced, inside thesingle crystal there exist regions often having oxidation stackingfaults caused by oxygen which is generated during oxidation heattreatment (hereafter OSF occurrence region). If using wafers picked outfrom such an OSF occurrence region in the heat treatment process of thesemiconductor IC production, OSF occurs and rejected chips is theconsequence.

Therefore, for supplying a wafer fitting these specific semiconductorproduction conditions, semiconductor production is performed by usingmany kinds of quality samples for pulling up the conditions; theperformance of the pull up at optimal conditions for product yield isnormally done in the high integration semiconductor production.

Furthermore, for preventing specific semiconductor production conditionsunder which OSF frequently occurs, heat treatment is performed byassuming the riskiest conditions, and after the heat treatment, the OSFdensity is decided. Therefore, abnormal OSF occurrence regions areeliminated in an afterprocess; the single crystal undergoes slicing;samples are taken out from these slices after being oxidation heattreated under conditions which are decided by the customer; they areexamined by sliced wafers and it is confirmed whether or not OSFoccurrence regions exist. If OSF occurrence regions exist, then theparts before and behind this one are considered as a malproduct. Inorder to survey the IG effect, simulation heat treatment reproducing theheat history of specific ICs is regularly carried out and a decision ismade on whether or not a change in the condition has occurred.

Furthermore, in prior art pull up methods for single crystals, not allof the various conditions for pulling up single crystals are recorded,even when the log record style is determined, record leaks and recordmisses cannot be avoided, and for all parts of single crystals thusobtained, it is usually difficult to accurately get hold of theinformation whether or not a region was in conformity with the demand ofthe customer.

Even when a quality test according to aforementioned sampling inspectionis performed, completely satisfying test results are not obtained andthere is demand for improvement.

SUMMARY OF THE INVENTION

The present invention takes into account the above describedcircumstances, and it is further an object of the present invention toprovide a method which allows the exact control of the position of themelt surface, as well as by suppressing the dispersion of the oxygenconcentration in axial direction, by which it becomes possible toproduce a uniform single crystal.

For this reason, in the present invention a signal is caused to fall onthe melt surface, the position of the molten liquid surface isdetermined by detecting the signal reflected from the molten liquidsurface, and the crucible is lifted according to the deviation from aset value.

When the signal is radiated on the melt surface, which has ripples dueto influences from the rotating crucible and the evaporating SiO, theincident signal is reflected at the molten liquid surface. Then, bydetecting this reflected signal, the position of the molten liquidsurface is measured, the crucible is lifted according to the deviationof the set value and the position of the molten liquid level can becontrolled. Though a change of the molten liquid surface is caused byheat variations of the crucible, the position of the molten liquid levelcan be exactly controlled, and the condition of the melt surface, thatis the growth surface of the single crystal, can be stabilized.Therefore, a single crystal having constant parameters, such as oxygenconcentration in axial direction, can be produced.

It is another object of the present invention to measure the temperatureof the liquid level accurately when molten, to detect that the moltenliquid current is in a stationary state, and furthermore to be able toproduce automatically a crystal without dislocations in the seed processwhere a seed crystal in the molten liquid is dunked in and thinly drawnup, by accurately controlling the temperature of the melt level at a settemperature, which is based on the aforementioned temperature.

Therefore, in the present invention, the surface temperature of theliquid is measured by taking the radiation energy ratio at two differentwavelengths in the infrared emitted by the molten liquid surface. Theheater current is regulated according to the deviation from the setvalue and the liquid surface temperature is controlled.

For measuring aforementioned melt temperature, it is advisable to makeuse of two thermometers which measure the molten liquid temperature bytaking the radiation energy ratio at two different wavelengths in theinfrared, emitted from the molten liquid surface.

Because for measuring the melt surface temperature by taking theradiation energy ratio at two wavelengths in the infrared region, whichare radiated from the melt surface when molten, in the pull up methodfor single crystals of the present invention, even if there iscondensation on the window with raw material gas originating from themolten liquid surface and the radiation intensity varies, bothwavelengths are influenced in the same way and the radiation energyratio at these two wavelengths does not change. For this reason, thetemperature of the molten liquid surface can be accurately measured,independent of external factors, such as condensation on the window.

According to the single crystal growth method of the present invention,the molten liquid surface temperature of the raw material solutionuneffected by external factors, such as precipitation on the window, canbe exactly measured.

According to the single crystal growth method of the present invention,overheating by overshoot cannot occur and the liquid cannot evaporateexcessively. Since it is possible to accurately control the temperatureof the liquid surface because of the aforementioned reason, a singlecrystal of determined shape and quality can be produced. Moreover, sincethe liquid surface temperature of the raw material solution can beaccurately controlled with respect to time, automatic setting of timingfor dipping the seed crystal into the molten liquid is possible whichhas the consequence that the manufacturing process can be automated. Bymeasuring and controlling the liquid surface temperature, even duringthe draw up, the pulling speed can be stabilized and a silicon singlecrystal of very high quality may be produced.

It is another object of the present invention to surely get hold of thesingle crystal lot region which does not meet the conditions of thecustomer, and to provide a single crystal growth method which enables toimprove quality reliance and stability.

Therefore, in the single crystal growth method of the present invention,data related to the draw up conditions during the pulling are detectedand stored; the start time of each process during the draw up process isdetected and stored; aforementioned stored survey data are compared withtheir beforehand stored corresponding tolerances; by outputting datafailing the tolerances as nonconformity pulling information, afterfinishing the draw up it becomes possible to detect regions inside thesingle crystal which fail the draw up conditions; and furthermore alldraw up data are conserved.

According to the single crystal growth method of present invention, itis impossible that operator entries are omitted or entry misses occur,and by comparing the observation data with the standard set values bymeans of computer processing, at the end of the pull up, it is possibleto get hold of the parts failing the condition of the single crystal dueto abnormal operation conditions which remain undetected in prior artlogs. Then, in the slicing process following the pull up process,nonconform regions may immediately be excluded, and in an after process,nonconform regions can be prevented to be supplied.

Accordingly, regions failing the conditions as well as crystal lots notmeeting the manufacturing conditions of the customer, may accurately beattained, and quality reliance and stability can be improved.Furthermore, by using the method of the present invention, it ispossible to attain the status quo of the single crystal pull up from acentral control room; malfunctions and mistakes of the pull up procedurecan be corrected quickly by a supervisor via remote control if thereoccur abnormalities in the manufacturing process, such as a sharplydecreasing yield rate, or interruptions in the process continuation,though the shipping was judged to meet quality standards and has notshown any abnormals, it is possible to call immediately those data onthe screen which lie back a reasonable period of time which gives thepossibility to recheck the detailed history of the draw up, to specify acrystal lot pulled up under identical conditions or exclude the onescurrently in the manufacturing process. Furthermore, if there appeardifferences in identical semiconductor manufacturing conditions within acrystal lot, it is possible to newly discover the relation between theoperation, which was formerly overlooked, and the single crystalquality, by comparing and examining these data, and single crystal drawup conditions which are most suitable for a variety of semiconductormanufacturing conditions may be set. These are the most importanteffects of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of an equipment which is an example forthe implementation of the single crystal growth method stated in claim4.

FIG. 2 is a flowchart showing the process of the first preferredembodiment,

FIG. 3 is a flowchart showing the first process of the liquid surfacecontrol method.

FIG. 4 is a flowchart showing the second process of the liquid surfacecontrol method.

FIG. 5 is a graph showing the dispersion of the oxygen density in axialdirection of the silicon single crystal manufactured according to thesecond preferred embodiment.

FIG. 6 is a graph showing the dispersion of the oxygen density in axialdirection of the silicon single crystal manufactured according to acomparative example.

FIG. 7 is a schematic diagram showing an example of an equipment forimplementing the single crystal growth method of claim 5.

FIG. 8 is a flowchart for explaining the melt process.

FIG. 9 is a flowchart for explaining the setting process.

FIG. 10 is a block diagram for explaining the simulation method by deadtime+first order delay process step response (PROC).

FIG. 11 is a block diagram for explaining the simulation method by deadtime+first order delay process feed back simulation (FEED).

FIG. 12 is a block diagram for explaining the simulation method by deadtime compensation feed back simulation (COMP).

FIG. 13 is a graph showing the simulation effect by dead time+firstorder process step response (PROC).

FIG. 14 is a graph showing the simulation effect by dead time+firstorder delay process feed back simulation (FEED),

FIG. 15 is a graph showing the simulation effect by dead timecompensation feed back simulation (COMP).

FIG. 16 is a graph showing the simulation effect by the same dead timecompensation feed back simulation (COMP).

FIG. 17 is a schematic construction diagram showing the operationcondition supervising system of the equipment implementation of thefirst preferred embodiment of the single crystal growth method fromclaim 7.

FIG. 18 is a cross section drawing showing the pulling apparatus mainbody comprising the equipment implementing the first preferredembodiment of the single crystal growth method of claim 7.

FIG. 19 is a flow chart showing the first preferred embodiment of thesingle crystal growth method of the present invention.

FIG. 20 shows the screen to which all tolerance fluctuation rateparameters are input.

FIG. 21 is a graph where the seed growth speed is displayed in the axisof ordinate and the draw up length in the axis of abscissa.

FIG. 22 shows the screen display of the operation condition.

FIG. 23 is a schematic diagram for explaining the relation betweenpulling speed and formations of OSF occurrence regions.

FIG. 24 is a schematic diagram for explaining the relation between theratio of seed rotation frequency and crucible rotation frequency andORG.

FIG. 25 is a figure from the output of the printer showing the parts forwhich the seed growth speed is out of tolerance.

PREFERRED EMBODIMENTS OF THE INVENTION

Hereinafter, a detailed explanation on the single crystal growth methodof the present invention is given by reference to the figures.

First preferred embodiment

FIG. 1 shows an example of the single crystal pulling equipment used forimplementing the single crystal growth method according to claim 4.

In this figure, there is a furnace main body 1; and roughly in thecenter of this furnace main body 1 a quartz crucible 2 is provided. Inthe inner part of this quartz crucible 2, the single crystal rawmaterial is allocated and becomes the molten liquid 6 when dissolved.Furthermore, this quartz crucible 2 is installed via a graphitesusceptor 3 on a lower axis 4, which can move up and down and rotate.Then, a carbon heater 7 controlling the temperature of the molten liquid6, which is contained in the quartz crucible 2, is provided in thevicinity of aforementioned quartz crucible 2. Moreover, an insulationtube 8 is installed between heater 7 and furnace main body 1. In thisinsulation tube 8, a tube shaped radiation heat shielding body 11 issupported by a plurality of engagement parts. This radiation heatshielding body 11 is tapered in downward direction. This radiation heatshielding body prevents changes of the heat history of the pulledcrystal, has the function of preventing impurities, such as CO gasoriginating from e.g. heater 7, enter the single crystal. The distancebetween the liquid surface and the tip of the radiation heat shieldingbody 11 must accurately be set in order to standardize the current pathof the gas.

Furthermore, a single crystal cooling pipe 10, which is water cooled, isattached to the neck part 14 of furnace main body 1. This single crystalcooling pipe 10 sticks out into furnace main body 1 and serves forcontrolling the heat history of the silicon single crystal during thepulling. Between the aforementioned single crystal cooling pipe 10 andthe neck part 14 of furnace main body 1, the pipe shaped gas currentpath is being formed. Furthermore, in the inner part of this singlecrystal cooling pipe 10 and neck part 14 of furnace 1, a wire 9 holdingthe seed crystal 5 and performing the draw up, is fixed in a hangingposition and can freely move up and down and rotate. Next a feed pipe 20for supplying Argon gas to the inside of single crystal Cooling pipe 10is connected to the upper end of aforementioned neck part 14.Furthermore, a window 12 is provided in the shoulder part of furnacemain body 1.

Furthermore, a laser light source 13 for radiating laser light on thesurface of molten liquid 6, a focus lense 15 for focusing the laserlightreflected at the molten liquid surface 6 and an optical sensor 16 forabsorbing the focused reflected light are provided in the outer part ofaforementioned furnace 1. In the outer part of furnace main body 1,there are further provided: a monitor 17 displaying the differencebetween the set value and the molten liquid surface position to whichthe electric current signal output by optical sensor 16 was converted, afeedback control apparatus for feeding back this difference, and acrucible control apparatus 19 controlling the position of the crucible.

When producing a single crystal by using the single crystal pullingequipment constructed as mentioned before, argon gas is put into furnacemain body 1 via aforementioned feed pipe 20; the ambient inside thefurnace main body 1 is substituted by argon gas; the single crystal rawmaterial which was placed beforehand into the inside of quartz crucible2 is dissolved to molten liquid 6 by means of heater 7; and then thetemperature of molten liquid 6 is maintained at an adequate temperaturefor the single crystal pulling (melting process).

Next, wire 9 is lowered and the lower surface of seed crystal 5, whichis positioned at the lower end of wire 9, is brought in direct contactwith molten liquid 6. Thereafter, quartz crucible 2 and seed crystal 5are caused to rotate in opposite direction of each other, and by pullingwire 9 at a constant speed, the growth of the single crystal at thebottom end of seed crystal 5 is initiated. In the meantime, at everysecond interval of a certain period, laser light is emitted from laseremitting apparatus 13 and caused to fall on the liquid surface of themolten liquid 6. The laser light reflected on the liquid surface isfocused by focus lense 15, outputted as electric current signal byoptical sensor 16, and then this electric current signal issimultaneously converted to the liquid surface position value anddisplayed at monitor 17 if the liquid surface position deviates from theset value, it is fed back to crucible control apparatus 19 by feed backcontrol apparatus 18, quartz crucible 2 having constant speed is movedupwards by crucible control apparatus 19, and the surface of moltenliquid 6 is controlled (seed process).

Moreover, at the time just before the diameter of the pulled singlecrystal becomes constant and the liquid surface position measured byaforementioned laser-light is equal to the set value, quartz crucible 2is elevated at constant speed by crucible control apparatus 19. When theposition of the molten liquid level is higher than the set value, quartzcrucible 2 is lifted with a crucible lifting speed which is decreased bya fixed ratio when compared with the aforementioned constant speed. Whenthe position of the molten liquid surface is lower than the set value,the quartz crucible 2 is lifted with a crucible lifting speed which isincreased by a fixed ratio when compared with the aforementionedconstant speed. Thus, the position of liquid 6 is controlled (shoulderprocess).

Proceeding like this, while controlling the liquid surface position ofmolten liquid 6, the silicon single crystal is drawn up and due to theapproach of the shoulder part of the silicon's single crystal upper partto the tapered opening of radiation heat shielding body 11 and to thelower end of crystal cooling pipe 10, the current path resistance of theargon gas, which is streaming downwards at the inner part of singlecrystal cooling pipe 10, increases, but because the argon gas fluxflowing through branch pipe 21 increases and the amount of gas, whichcontains heated SiO and is located between the molten liquid and theradiation heat shielding body 11, is increased, consequently, a suddenchange in the flow of argon gas supplied to the crystal growth surfacecan be suppressed. Accordingly, there is no sudden temperature change inthe crystal growth face neighbourhood of the quartz crucible 2 and theventilation of SiO coming from molten liquid 6 can be smoothly put intopractice, crystal defects don't occur, and it is possible to pulled thesilicon single crystal such that the variation of oxygen density stayssmall.

If a single crystal has been pulled to the desired length according tothe aforementioned procedure, the liquid surface control is stopped, thepower for heater 7 switched off and the draw up of the single crystal isterminated (bottom process).

Next, the operation procedures in all the aforementioned processes areonce more explained in detailed by following the flow-charts from FIG. 2to FIG. 4.

1. Melting process

First, the solving process SW is put on, power of heater 7 is put on(step 30), and by dissolving the single crystal raw material, which isput into the quartz crystal crucible 2, molten liquid 6 is obtained.Next, after having made sure that the crucible position is above thezero point position (step 32), the power source for laser emittingapparatus 13 is switched on (step 34). At this point, the vacuum gauge(not shown in the figure) provided inside the furnace main body I isswitched off when there is an atmosphere. Furthermore, the display ofmonitor 17 for the liquid level position is started (step 36).

2. Seed process

Next, wire 9 is lowered and the lower surface of seed crystal 5, whichis attached to the lower end of wire 9, is brought into contact withmolten liquid. After this, quartz crucible 2 and seed crystal 5 arecaused to rotate in opposite direction (seed rotation on, cruciblerotation on), and by drawing up wire 9 at constant speed the growth ofthe single crystal at the lower end of seed crystal 5 is being started(slow seed lifting on) (step 38). When at this point eitheraforementioned seed rotation, crucible rotation or slow seed lifting isput off, the control is stopped and sent back to step 32 of dissolutionprocess 1.

After step 38, the first liquid level control is executed (step 40). Onthe subject of this liquid level control method, detailed explanationsare given by following the flow chart in FIG. 3.

At the beginning of this liquid level control, it has to be checkedwhether the following conditions are satisfied (liquid level controlstart conditions).

a) Laser liquid level control flag is set.

b) Power of heater seven is available.

c) The inside of crucible main body 1 is decompressed below a certainpressure.

d) The position of the crucible is set above the zero point.

e) The seed rotation, crucible rotation and slow seed lifting isswitched on.

If it is certain that among the conditions a to e conditions a, b, c, dare satisfied (Yes case of step 41), the laser light emitted from laseremitting apparatus 13, whose interval is set to a sampling time of 0.1sec., falls on the surface of molten liquid 6; the laser-light reflectedby the liquid surface is focused by focus lense 15 and the absorbedvalue is sampled with optical sensor 16. Furthermore, for smoothing theliquid surface position, 50 sampling data are accumulated; the averageof these 50 data is taken and displayed as liquid surface position atmonitor 17 (step 42, step 43).

Next, if condition e is satisfied, liquid surface control is started(Yes case of step 44).

First, the response time (interval of time which is fed back to cruciblelift) is set to 10 seconds. When this time has passed (step 45), it isdetermined whether or not the liquid level position lies within theliquid level shift tolerance value of 0.1 mm (step 46).

In case the liquid level position lies outside the range of liquid levelshift tolerance value, the crucible lifting speed is increased to 0.05mm/min (step 47), and if the liquid position lies within the liquidlevel shift tolerance value (No case of step 6), the lifting of thecrucible is stopped (step 48).

After step 48 is terminated, step 50 shown in FIG. 2 follows next.

On the other hand, if in step 41 not each of the steps a to d aresatisfied, there is a jump back to step 30 in FIG. 2. If furthercondition e in step 44 is not satisfied, there is a jump back to step 38shown in FIG. 2.

3. Shoulder Process

Furthermore, the diameter of the drawn up single crystal (shoulderdiameter) is detected, and it is determined whether it became equal tothe diameter which set the crucible lifting start (step 50 of FIG. 2).If it equals the set diameter, the crucible lifting starts (step 52) andthe second level liquid control is performed (step 60).

If on the other hand the shoulder diameter does not match the setdiameter (No case of step 50), the first liquid level control process ofstep 40 is repeated.

A detailed explanation of the second surface liquid control method isgiven by following the flowchart shown in FIG. 4.

First, when starting the second liquid surface control, it is checkedwhether the conditions stated hereafter are satisfied (liquid surfacecontrol start condition) (step 61).

f) Performance of first liquid surface control.

g) The shoulder diameter becomes equal to a beforehand set diameter, thecrucible is lifted and the start of the second liquid surface controlcan be prepared.

If, on the other hand, one of the conditions f, g is not satisfied (Nocase of step 61), there is a jump back to step 40 in FIG. 2, and ifconditions f, g are satisfied (Yes case of step 61), after passing theresponse time of 10 seconds (step 62), it is determined whether theliquid level position lies in the liquid level shift tolerance value of0.1 mm (step 63).

if the liquid level position lies within the range of the liquid levelshift tolerance value (No case of step 63), step 70 follows, thecrucible is lifted at the crucible lifting speed (hereafter calledstandard crucible lifting speed), which is calculated by (seed liftingspeed)×(crucible lifting ratio). (In other words, ratio correction valueof crucible lifting is 0).

On the other hand, if the liquid level position does not lie within therange of the liquid level shift tolerance value (Yes case of step 63),the liquid level control described hereafter is performed.

First, when the liquid level position is lower than the liquid level setvalue, the crucible lifting speed is corrected by increasing the liftingspeed with a correction ratio of only 5% (step 64). The response time is10 seconds (step 65). By repeatedly performing liquid level measuring,it is determined whether it lies within the range of the shift tolerancevalue (step 66); if the liquid level position lies repeatedly under theliquid level set value (Yes case of step 66), the correction ratio isnewly added, and there is an increase towards the standard cruciblelifting speed of a 2×5% correction value part lifting speed. Proceedinglike this, the correction ratio is added to the crucible lifting speeduntil the liquid level position becomes the liquid level set value, inother words, in the meantime, when there occurs n times such acorrection, the crucible lifting speed is increased by correction valuen×5% when compared with the uncorrected value (step 68). This correctioncontinues until n×5% becomes the ratio correction limit value (No caseof step 69). If the liquid level position enters the range of the shifttolerance value before it becomes equal to the ratio correction limitvalue (No case of step 66), it is decided whether the liquid levelposition is below 0 (step 67), and if the liquid level position is below0 (Yes case of case 67), step 70 follows. Furthermore, if the liquidlevel position is greater than 0 (No case of step 67), there is a jumpback to step 64, and the correction of the crucible lifting ratio isrepeatedly performed.

On the other hand, if the liquid level position of molten liquid 6 ishigher than the liquid level set value, the crucible lifting speed isstepwise decreased by the correction ratio (5%), and the lifting speeddecreases. In other words, if there are n corrections until reaching theliquid level set value, the crucible lifting speed is decreased bycorrecting it n×5% (step 68). Then, if the liquid level position reachesthe shift tolerance value (No case of step 66) and the liquid levelposition is below 0 (Yes case of step 67) or n×5% exceeds the ratiocorrection limit value, the standard crucible lifting speed before thecorrection is reactivated, and the crucible is lifted (step 70). Afterstep 70, step 80 displayed in FIG. 2 follows.

4. Bottom process

After having performed the draw up of the single crystal describedhereinafter, it is confirmed whether-the draw up has reached apredetermined value (step 80). If the single crystal has not been drawnup to a predetermined length (No case of step 80), there is a jump backto the second liquid control process of step 60. If the crystal has beendrawn up to a predetermined length (Yes case of case 80), the bottomprocess is switched on (step 82), and thereafter, the bottom end orPower Off is reached (step 84), the laser power source is switched off(step 86), the liquid surface position monitor is switched off (step 88)and the single crystal draw up is finished.

This liquid surface control method makes use of causing laser light tofall on to the liquid surface of molten liquid 6 at the time of draw upgrowth of the single crystal, and by detecting the reflected light fromthe surface, the shift from the set value of the liquid surface positionis measured, and since there is a method lifting the crucible accordingto this shift, it is possible to exactly control the liquid levelposition even in the shoulder forming process (seed process) which wasdifficult to be controlled by hitherto liquid level position controls.Even if there occurs a change in the liquid level position of moltenliquid 6 by heat deformation of quartz crucible 2, the liquid levelposition can be controlled more accurately, and it becomes possible tostabilize the molten liquid surface, or in other words, the condition ofthe single crystal growth surface. By using the radiation heat shieldingbody board and by drawing up the single crystal, a single crystal can beproduced so that the variation of the oxygen density in axial directionbecomes smaller.

Second preferred embodiment

By using the apparatus of the first preferred embodiment, a siliconsingle crystal was produced.

At a pressure of 10 Torr inside furnace main body 1 and an argon gasflux of 30 Ni/min, 50 kg of polycrystal silicon are dissolved in thequartz crucible 2, which has a diameter of 16 inch. After thetemperature of molten liquid 6 inside the quartz crucible 2 has reacheda level where it is possible to perform the draw up, wire 9 is loweredand seed crystal 5 is brought in direct contact with molten liquid 6.Then the revolution speed of seed crystal 5 is set to 22 rpm, therevolution speed of quartz crucible 2 to 5 rpm, and the silicon singlecrystal is drawn up at a speed of approximately 1.5 mm/min.

From the time when the dissolution of the raw material has finished,laser is shone on the liquid surface by laser equipment apparatus 13,the liquid position of molten liquid 6 is 50 times sampled in aninterval of 0.1 sec, and the molten liquid position is smoothed. Thenthe shift tolerance range is set to +0.1 mm. If there is a deviationbeyond this margin, feed back control equipment 18 is put into action. Aone time correction of the crucible lifting speed is set to +0.5% andthe limit value where the crucible lifting speed can be corrected is setto +20%. The time interval from measuring the liquid level to thecontrol of the crucible shifting speed is set to 10 seconds. Bycontrolling the liquid level position of molten liquid 6 in such a way,it was possible to take the difference between the liquid level shiftand the set value within a range of 0.1 mm during the control processperiod.

The oxygen density dispersion in axial direction of the silicon singlecrystal obtained from this example is shown in FIG. 5. Furthermore, theoxygen density in axial direction of the silicon single crystal producedaccording to the former ratio control is shown as a comparative example.

As a result of this, it was confirmed that the oxygen density in axialdirection stayed roughly constant when control of the molten liquidsurface was performed by laser.

Third preferred embodiment

FIG. 7 shows an example of a single crystal pulling apparatus forimplementing the single crystal growth method according to claim 5.

In this figure, identical signs are attached to similar constructionparts for simplifying explanations.

Points at this apparatus which differ from the apparatus of the firstpreferred embodiment, are the points following hereafter, whereas theother parts are similar to the ones of the first preferred embodiment.

In the inner part of aforementioned furnace main body I an ADC sensor 24for measuring via window 12 the diameter of the silicon single crystalto be pulled up and a line camera 25 are provided.

Furthermore, a window 23 is provided at the side part of furnace mainbody 1. Via this window 23, ATC sensor 27 measures the temperature ofheater 7. On the upper part of neck part 14 of furnace main body 1, adichromatic thermometer 26 for measuring the temperature of moltenliquid 6, is provided. To this dichromatic thermometer there areconnected, a computer system 28 which determines the power for heater 7by PID control according to the result obtained by calculating thediscrepancy between the measured temperature and the set temperature,and an SCR controller 29 controlling the power for heater 7.

If a single crystal draw up apparatus constructed like the one mentionedbefore is used and a single crystal is produced, first, valve 21 isactivated, and at a fixed manufactured opening, argon gas is fed intothe inner of furnace main body 1 via aforementioned feed pipe 20 andbranch pipe 22, and while the ambient inside furnace main body 1 isreplaced by Argon gas, the single crystal raw material which was putbeforehand into quartz crucible 2, is dissolved by heater 7 (dissolvingprocess). Inside quartz crucible 2, the temperature control for thesingle crystal raw material melting period is performed as describedabove.

The liquid surface temperature is measured by using a dichromaticthermometer 26, which is attached to the outer part of furnace main body1, yields the reflected energy ratio of two waves which are reflected bythe molten liquid surface at the time of dissolving and have differentwavelengths in the infrared. The heater power corresponding to thediscrepancy between the liquid level temperature and the set temperaturecomes from SCR controller 29 backed up by the PID control in computersystem 28 and is applied to heater 7. Thus, the liquid surfacetemperature is regulated to the set temperature.

After having maintained the temperature of dissolved, molten liquid 6 atthe set temperature suitable for the single crystal pulling, wire 9 islowered and the seed crystal attached to the bottom end of wire 9 isdipped into molten liquid 6. Then, by pulling the seed crystal, whilequartz crucible 2 and the seed crystal rotate in opposite directions,the silicon single crystal 5 is caused to grow at the bottom end of theseed crystal (seed process).

Since the shoulder part in the upper part of silicon single crystal 5approaches the bottom end of single crystal cooling pipe 10 and theopening part of radiation heat shielding body 11, which is shrunken indiameter, at the time when the silicon single crystal 5 is pulling inaforementioned way, the flow path resistance of the argon gas flowingdown the inner part of single crystal cooling pipe 10 increases. Sincethere is an increase in both, the flux of argon gas streaming throughbranch pipe 22 and the amount of gas containing heated SiO and locatedbetween the molten liquid and the radiation heat shielding body 11, as aresult, a sudden change in the flow of argon gas supplied to the crystalgrowth surface is suppressed. Therefore, a sudden temperature change inthe single crystal growth surface vicinity inside quartz crucible 2 doesnot occur, the ventilation of SiO from molten liquid 6 is smoothed, thecrystal has no dislocations, and it is possible to proceed with the drawup of silicon single crystal 5, so that there are only small variationsof oxygen concentration.

Though it is possible to grow a silicon single crystal 5 of surpassingquality by the aforementioned method, a detailed explanation on theprocess controlling the liquid surface temperature to the settemperature before dipping the seed crystal into molten liquid 6, isgiven by the flow-charts in FIG. 8 and FIG. 9.

First, an explanation on the dissolving process for dissolving thesingle crystal raw material is given by following the flow chart of FIG.8.

The SW of the dissolving process is switched on (step 130), the heaterpower source is switched on and the voltage of heater 7 is raised to afixed value. At the time when the heater power source is switched on,time is set to 0 (step 132).

Then, the use of the dichromatic thermometer 26 and the smoothing of theliquid level temperature is started (step 134 of FIG. 8). If thedecision whether the crucible rotation starting time has passed is Yes(step 136), the crucible rotation is started (step 144). If thisdecision is no, and the decision on whether the liquid surfacetemperature has reached the set temperature where the crucible can berotated (step 138) is Yes, it is decided whether or not the delay timeuntil the crucible may be rotated has passed (step 140). If the answerto step 140 is Yes, step 144 follows next and the crucible rotation isstarted. On the other hand, if the answer to step 138 is No, there is ajump back to step 134, and if the answer to step 140 is No, step 144follows after the delay time until the crucible rotation can be started(step 142) has passed.

In step 144, the number of revolutions of quartz crucible 2 is increasedto the set rotation value by a process described hereinafter.

First, after having confirmed that the crucible rotation starting timehas passed since the set time, the message of rotation start inquiry isoutput and by detecting the crucible rotation switch on On, the cruciblerotation start is confirmed.

Second, after the crucible rotation switch is set on On, by controllingthe crucible rotation motor, the number of revolutions of the crucibleis slowly increased until the set revolution number is reached.

When the crucible revolution number has reached the set revolutionnumber, it is decided whether the delay time for lifting the cruciblehas passed (step 146). If the answer is Yes, step 156 follows and thecrucible lifting is started. If the answer is No, it is decided whetherthe delay time for the set temperature confirmation where the cruciblecan be lifted has passed (step 148); if the answer is Yes, it isdecided-whether the crucible has reached the temperature where is can belifted (step 152). In case the answer to step 152 is Yes, step 156follows and the crucible lifting is started. On the other hand, if theanswer to step 148 is No, step 152 follows after the delay time for theset temperature confirmation where the crucible can be lifted has passed(step 150). If the answer to step 152 is No, step 156 follows a pauseuntil the set temperature where the crucible can be lifted is reached(step 154).

In step 156 the crucible lifting is started, and lifted continuously toa beforehand set crucible lifting distance. Next, heater 7 is powereddown to a fixed value (step 158), the liquid surface temperature isdetected by dichromatic thermometer 26, and it can be decided whetherthe dissolution end temperature is exceeded (step 160).

if the answer to step 160 is Yes, it can be decided whether the setprocess is switched on (step 164); if Yes, the later stated set processis run. If No, a message of termination is output (step 166 ).

If the answer to step 160 is No, step 164 follows after waiting untilthe dissolving end temperature is reached (step 162).

Next, a detailed explanation on the set process by following the flowchart in FIG. 9 is given.

First, in step 180, it is checked whether ATC sensor 27 is normal. Thischeck is performed by detecting the temperature of heater 7 by ATCsensor 27, and if the detected temperature is lower than the lower limitof ATC sensor 27 (No case of step 180), an error message is displayed(step 182). If the temperature detected by ACT sensor 27 is higher thanthe lower limit of ATC sensor 27 (Yes case of step 180), step 184follows next, and it is checked whether dichromatic thermometer 26 is innormal condition. This check is executed by detecting the liquid surfacetemperature with dichromatic thermometer 26. If the detected temperatureis different from the set liquid surface temperature (No case of step184), an error message is output (step 186). If the detected temperatureis equal to the set liquid surface temperature (Yes case of step 184),step 188 follows next and the position of quartz crucible 2 is set.

After termination of step 188, the liquid surface temperature is set(step 190). This setting is performed as described hereinafter.

First, the liquid surface temperature is detected by dichromaticthermometer 26, and the difference to the set liquid surface temperatureis fed back to the power supply of heater 7 by controlling the SCRcontroller. However, the liquid surface temperature is input once in 0.5seconds and by the calculation stated hereafter PID control isperformed. ##EQU1## whereby difference n=liquid surface temperaturen-set liquid surface temperature,

P const=(P const of set process parameter)/100,

I const=10000/(I const of set process parameter),

D const=(D const of set process parameter)/10,

time const=(time const of set process parameter)/100

Δt=(sampling time of set process parameter)/100,

t=0˜Δt

The calculation method for the dead time compensation value is shownhereafter.

F1,n=F1,n-1+(T_(S) /T)×(Cn-F1,n-1)

F2,n=F2,n-1+2×(T_(S) /L)×(F1,n-F2,n-1)

F3,n=F3,n-1+2×(T_(S) /L)×(F2,n-F3,n-1)

Cn:heater power n-bias

Ts: (sampling time of set process parameter)/100

T:(process time constant of set process parameter)/100×60

L:(process dead time of set process parameter)/100×60

Dead time compensation value=A×(F1,n-F3,n)

A:process gain of set process parameter/100

Then, secondly, for detection recristallisation, an error message isoutput if the liquid surface temperature is below 1400° C.

Thirdly, it is confirmed and finally established that the liquid surfacetemperature lies within ±1° C. of the set liquid surface temperature andthat the termination decision time is reached.

After finishing step 190, it is decided whether the switch of the seedprocess is on On (step 192), and if Yes, the seed process is put intoaction. If the answer is No, a termination message is output (step 194).

The liquid surface temperature before the seed process (process ofdipping the seed crystal into molten liquid 6) is controlled to the settemperature as described hereinafter.

Since in this single crystal draw up process the dichromatic thermometer26 is used for measuring the liquid surface temperature by taking theenergy ratio of two waves having two wavelengths in the infrared andwhich are reflected from the molten liquid surface at the time ofmelting, the temperature of the molten liquid surface of the rawmaterial melting, which is not influenced by external factors such asprecipitation on the window, can be exactly measured. Therefore, bycontrolling the heating power in accordance with the difference betweenthe measured temperature and the set temperature, there occurs nooverheating by overshoot and molten liquid cannot evaporate excessively.

Moreover, since in this single crystal pulling process, due toaforementioned reasons, the temperature of the surface liquid can beaccurately controlled and a single crystal of constant shape and qualitymay be manufactured.

Furthermore, since in this single crystal manufacturing method, theliquid surface temperature of the raw material melting and time can beaccurately controlled, the timing for dipping the seed crystal into themolten liquid can be set on automatic, and the seed process can beautomated.

Hereinafter, some more explanations are given on the method for decidingby simulation the liquid surface control parameters in preferredembodiment 4 to 6.

Fourth preferred embodiment

FIG. 10 shows the simulation method for dead time plus linear delayprocess step response (PROC).

When the process transmission function is set to

    (A e.sup.-LS)/(1+TS)

as indicated in FIG. 10 (whereby, A:process gain, L:process dead time,T:process time constant, S:process operator), process variable PV iscalculated when control input C is input and output at the frequency/ofthe unit time.

The calculation is carried out according to the difference formulasstated hereafter, which replace the transmission function of the Laplacedescription.

Process

F1,n=F1,n-1+(T_(s) /T)×(Cn-F1,n-1)

F2,n=F2,n-1+2×(T_(s) /L)×(F1,n-F2,n-1)

F3,n=F3,n-1+2×(T_(s) /L)×(F₂,n-F3,n-1)

PV=AF3,n

Here, T_(s) is the sampling time.

In FIG. 13, the simulation result is shown for T_(S) =30 sec, L=600 sec,T=1500 sec, A=0.3.

As a result of this, the graph of the obtained time--process variabledoes not overshoot and reaches the setting time of the target value inapproximately 100 min.

Fifth preferred embodiment

FIG. 11 shows the dead time+linear delay process feed back simulation(FEED) method. As shown in FIG. 11 the transmission function of theprocess is set to

    (A e.sup.-LS)/(1+TS)

and the transmission function of the PID control to

    K(1+(1/T.sub.I S)+T.sub.D S)

(whereby, K:comparison gain, T_(I) :integral time, T_(D) :differentialtime), and when the process variable (PV) is controlled by feed back soit equals the target value (SP), control input (C) and process variable(PV) are calculated and are repeatedly output after each unit time.

Calculation is performed by substituting the transfer function of theLaplace description with the difference form stated hereafter.

PID controller

EN=PV-SP

Vn=(T_(S) /2)×(En+En-1)+Vn-1

C=K((En+(VniT_(I))+(T_(D) /Ts)×(En-En-1))

process

F1,n=F1,n-1+(T_(S) /T)×(Cn-F1,n-1)

F2,n=F2,n1+2×(T_(S) /L)×(F1,n-F2,n-1)

F3,n=F3,n-1+2×(T_(S) /L)×(F2,n-F3,n-1)

PV=AF3,n

If K=-20, T_(I) =714 sec, T_(D) =360 the simulation effect shown in FIG.14 is obtained.

As a result of this, the graph of the obtained time and process variableconfirms that the set time to the target value is approximately 80minutes and though it is comparatively small to the one in the firstpreferred embodiment, there is an overshoot.

Sixth preferred embodiment

FIG. 12 shows the dead time compensation feed back simulation (COMP).

When the transfer function of the process, as indicated in FIG. 12, is

    (A e.sup.-LS)/(1+TS)

the transfer function of the PID controller is

    K(1+(1/T.sub.I S)+TDS)

and the transfer function of the dead time compensation is

    (A'(1-e.sup.-L's))/(1+T'S)

(for A': model process gain, L': model process dead time, T': modelprocess time constant),

and when the process variable (PV) controlled by feed back such that itequals the target value (SP), control input (C) and the process variable(PV) are calculated and are repeatedly put out at each unit time.

The calculation is executed by substituting the transfer function of theLaplace description by the difference form stated hereafter.

PID controller

EN=PV+D-SP

Vn=(T_(S) /2)×(En+En-1)+Vn-1

C=K((En+(Vn/T_(I))+(T_(D) /Ts)×(En-En-1))

process

F1,n=F1,n-1+(T_(S) /T)×(C-F1,n-1)

F2,n=F2,n-1+2×(T_(S) /L)×(F1,n-F2,n-1)

F3,n=F3,n-1+2×(T_(S) /L)×(F2,n-F3,n-1)

PV=AF3,n

dead time compensation

F'1,n=F'1,n-1+(T_(S) /T')×(C-F'1,n-1)

F'2,n=F'2,n-1+2×(T_(S) /L')×(F'1,n-F'2,n-1)

F'3,n=F'3,n-1+2×(T_(S) /L')×(F'2,n-F'3,n-1)

D=A'(F'1,n-F'3,n)

FIG. 15 shows the simulation results of the process variable for thecase that L'=300 sec, T'=900 sec, A'=0.1, K=-20, T_(I) =526 sec, TD=150sec. Furthermore, FIG. 11 shows the simulation result of the processvariables for the case that L'=600 sec, T'=1500 sec, A'=0.3, K=-50,T_(I) =400 sec, T_(D) =10 sec.

Though a change of the process variable could be seen in the resultdisplayed in FIG. 15, in the result displayed in FIG. 16 there is noovershoot and in approximately 30 minutes a saturation result at the setvalue can be achieved.

Seventh preferred embodiment

A temperature set experiment was performed by using the single crystaldraw up apparatus explained in the third preferred embodiment, a chargeamount of 40 kg, a crucible revolution speed of 5 rpm and by using theparameters obtained from the simulation results of FIG. 16. As a resultof this, as the heater power was limited to the range of 0-100 KW, thetime until the set value was reached was 69 minutes and therefore longerthan the simulation result in FIG. 15. However, it was possible toobtain a result which does not overshoot.

Eighth preferred embodiment

FIG. 17 and FIG. 18 show an example of an apparatus realizing thesilicon single crystal growth method according to the preferredinvention. This apparatus of FIG. 18 is a simplification of the draw upapparatus shown in the first and third preferred embodiment. In thisapparatus, a quartz crucible 2 is provided in the approximate centralpart of furnace main body 1. This quartz crucible 2 is installed viagraphite susceptor 3 on a lower axis 4 which can move freely up and downand can also rotate freely. In the surrounding of quartz crucible 2,heater 7 is provided for controlling the temperature of silicon moltenliquid 6 in the inside of quartz crucible 2. Wire 9, which holds anddraws up seed crystal 5, hangs over quartz crucible 2, can freely moveup and down and also rotate freely. When silicon single crystal 5 ispulling in furnace main body 1, first the air inside furnace main body 1is sufficiently replaced with argon gas; the raw material which was putbeforehand quartz in crucible 2 is melted by means of heater 7, thenwire 9 is lowered, so that the seed crystal dips in dissolved siliconmolten liquid 6, then quartz crucible 2 and the seed crystal are causedto rotate in opposite directions while wire 9 is lifted up and causessingle crystal 5 to grow.

To this furnace main body 1, as shown in FIG. 17, the pulling machinemicrocomputers 213 of the operation state observation system arerespectively connected. To this pulling machine microcomputers 213, thesensor of the mechanism driving wire 9 of furnace main body 1, thesensor of the mechanism driving crucible 2, heater 7, the thermometerinside the crucible--not shown in the figure--, the barometer inside thecrucible, the argon flux meter and all the other sensors for detectingconditions during the single crystal draw up are connected. Furthermore,the mechanism automatically detecting the starting times of all pulltreating processes run in furnace main body 1 are connected to thispulling machine microcomputer 213. The data sent to this microcomputer213 are stored temporarily in this microcomputer 213. The microcomputer213 is connected to minicomputer 215 via communication circuit 214. Thedata stored in microcomputer 213 are sent to minicomputer 215 viacommunication circuit 214. Minicomputer 215 is connected viaaforementioned communication circuit 214 with printer 216, which outputsdraw up error messages, and with terminal 217 displaying the receiveddata. Minicomputer 215 is connected to optomagnetic disk 218 storing thereceived data.

Now the first preferred embodiment for the silicon growth method of thepresent invention performed by this apparatus is explained in accordancewith the flowchart in FIG. 19. In the explanation following hereafter,Sn stands for n-th step in the flow-chart.

In this single crystal draw up process, the manufacturing of the singlecrystal is started, the survey data of the draw up conditions are shownin group A hereafter and were measured in a constant time interval byall sensors provided in furnace main body 1, and the starting time dataof all processes during the pulling which are shown in group Bhereafter, are sent to microcomputer 213. Furthermore, also such data assilicon charge amount inside the crucible at the beginning of thesilicon melt process, the leak rate of the gas inside the crucible, theposition of the crucible at the beginning of the shouldering process(position in the draw up direction) are sent to microcomputer 213 (S1).

Group A

seed lifting speed

crucible lifting speed

seed revolution number

crucible revolution number

heater temperature

inner pressure of furnace

Argon gas flux

Group B

vacuum process

dissolution process

seed process

shouldering process

cylindration process

bottom process

cooling process

process of carrying out manual operations on the lifting and lowering ofthe seed and the crucible

process of carrying out manual operations on the revolution of seed andcrucible.

Aforementioned data are temporarily stored in every microcomputer 213(S2). On the other hand, from minicomputer 215 a signal demanding datain a 10 min. interval is sent to each microcomputer 213 (S3), andaccordingly from every microcomputer 213 aforementioned data are sent tominicomputer 215 (S4). These data are stored on optomagnetic disk 218(S5).

Tolerance change ratio of all the parameters on the screen, shown as anexample in FIG. 20, are input to minicomputer 215. At the time when itis decided whether or not all parts of the manufactured single crystalsare suitable for shipping, aforementioned stored data are compared withthese tolerance ranges and then it is decided whether or not they fallwithin the tolerance range (S6). If they do not fall within thetolerance range, these parts are declared unsuitable for shipping; ifthey fall within the tolerance range, these parts are declared suitablefor shipping.

On the other hand, it becomes possible to display graphically the datataken in for every obtained single crystal as shown in FIG. 21. Thegraphic example shows the relation between the seed lifting speed andthe single crystal draw up length whereby the lines 220 and 221 indicatethe upper and lower limit for the tolerance range of the seed liftingspeed. The seed lifting speed is displayed whereby the data for astraight cylindrical part of the single crystal were processed forintervals of 10 mm. In other words, for every 10 mm drawn up part,maximum value, minimum value, average value, median and standarddeviation of the seed lifting speed at the draw up is known and can bedisplayed. In this graph, D,E,F show those parts for which maximumvalues and minimum values fall out of the tolerance range. Such areaswhere the seed lifting speed falls out of the tolerance range can alsobe confirmed by an output of printer 216 as shown in FIG. 25.

According to this operation condition observation system, such things asstarting time of each process during the single crystal draw up can bedisplayed and confirmed on terminal 217 as indicated in FIG. 22.

Since according to the single crystal growth method, the operationconditions during the single crystal manufacturing can automatically bedetected, entry leaks and entry misses by the operator may beeliminated, and by computer processing the comparison between surveydata and standard set values, it is possible to simultaneously get holdof those parts of the single crystal not meeting the standards, due toabnormal process conditions which did not remain in hitherto recordingsonce the draw up process was terminated.

If the pulling speed (seed lifting speed) showed abnormalities as shownin, for example, FIG. 23 (a), the formation of QSF occurrence regions224 in the single crystal, as indicated in FIG. 23 (b) can be detected.When the ratio of seed revolution number (SR) and crucible rotationnumber (OR) show abnormal values, it can be seen that the inplanedistribution ratio of the oxygen density ((center part oxygendensity--surrounding part oxygen density)/central part oxygen density;hereinafter called ORG) in this part, as indicated in FIG. 24, fallsoutside the tolerance range.

Then, the parts not meeting the conditions of the slicing process whichfollows the pulling process, are immediately excluded and in thefollowing process unsuitable parts may be prevented from beingdelivered. According to the single crystal growth method of thispreferred embodiment, it is possible to precisely get hold of thecrystal lot not meeting the manufacturing terms of the customer andportions which are not suitable, also reliability and stability ofquality can be improved.

What is claimed is:
 1. A single crystal growth method in which a siliconcrystal is grown from molten silicon liquid in accordance with theCzochralski method whereinsaid silicon crystal is coaxially surroundedby a tube shaped heat shielding body which is tapered in downwarddirection, laserlight is caused to fall on the molten liquid surfacethrough the inside of the tube shaped heat shielding body, the positionof the molten liquid surface is measured by detecting reflectedlaserlight coming from the molten liquid surface, and the position ofthe molten liquid surface is controlled whereby the crucible is liftedat a constant speed if the position of the molten liquid surface isequal to the set value, the crucible lifting speed is set to be saidconstant speed diminished by a fixed ratio if the position of the moltenliquid surface is higher than the set value, the crucible lifting speedis set to said constant speed increased by a fixed ratio if the positionof the molten liquid surface is lower than the set value whereby, when atemperature of the liquid surface of the single crystal raw material iscontrolled, the liquid surface temperature is measured by taking anenergy ratio of two waves having different wavelengths in the infraredand said two waves are emitted surface, and the liquid surfacetemperature is controlled whereby a heater power is regulated accordingto the difference to set temperature value.
 2. A single crystal growthmethod according to claim 1 wherebya right value of a control parameterrelated to a control of the liquid surface control, is determinedbeforehand by simulation and a value of said parameter is used tocontrol the liquid surface temperature.
 3. A single crystal growthmethod according to claim 2 whereby aforementioned data related to thepulling conditions consist of data of conditions listed hereafter ingroup A, the silicon charge amount inside the crucible at the siliconmelting process starting time, a leak rate of gas in the furnace, theposition in pulling direction of the crucible at the shoulder processstarting time of the single crystal, every process during said draw upprocess consists of processes listed in group B stated hereafter.GroupAseed lifting speed crucible lifting speed seed revolution numbercrucible revolution number heater temperature inner pressure of furnaceargon gas flux Group Bvacuum process dissolution process seed processshouldering process cylindration process bottom process coolingprocessprocess of carrying out manual operations on the lifting andlowering of the seed and the crucible process of carrying out manualoperations on the revolution of seed and crucible.
 4. The methodaccording to claim 1 whereby,data related to pulling conditions aredetected and stored during a draw up process, starting time of eachprocess during the pulling process is detected and stored, said detectedand stored data are compared in a comparison process with a tolerancerange of these data stored beforehand, such that by outputting the datafalling outside the tolerance range as draw up mismatch information, itbecomes possible to detect after draw up termination parts in the singlecrystal not complying with the pulling conditions, and all pulled dataare stored.
 5. A single crystal growth method whereby in the siliconsingle crystal growth methoda silicon single crystal is caused to growfrom a silicon molten liquid which was put into a crucible according tothe Czochralski method, data related to pulling conditions are detectedand stored during a draw up process, starting time of each processduring the pulling process is detected and stored, said detected andstored data are compared in a comparison process with a tolerance rangeof these data stored beforehand, by outputting the data falling outsidethe tolerance range as draw up mismatch information, it becomes possibleto detect after draw up termination parts in the single crystal notcomplying with the pulling conditions, and all pulled data are stored.